Wheel balancers reduce operational vibrations of vehicular tire and wheel assemblies by the calibrated placement of correction weights. An example of such a wheel balancer is the Hunter GSP 9700 Vibration Control System; for which the Operation Instructions, Software Version 1.3, Form 4202T, O7-99.COPYRGT. Copyright 1997 Hunter Engineering Company, is expressly incorporated herein by reference. Referring to Section 5 of the GSP 9700 Operating Instructions, vibrations in tire and wheel assemblies can be caused by: imbalance; non-uniform sidewall stiffness (force variation); bent or out-of-round rims; out-of-round tires and combinations thereof. The theory, analysis and correction of these factors with wheel balancers and the GSP 9700 in particular is described in the afore cited GSP 9700 Operating Instructions.
As described in a note of emphasis from Sect 2.2 OEM-Matching.TM. of the GSP 9700 Instructions: "It is important that the air pressure of the tire is set to specifications prior to the Road Force Measurement.TM.. Incorrect tire pressure will affect the results." It is also well known in the art that extreme tire pressure errors can cause imbalance measurement errors. Most importantly, tires which arc either over inflated or under inflated are likely to have premature failures resulting in possibly serious injuries.
Accomplishing pneumatic vehicle tire vibration reduction with a wheel balancer thus requires an accurate tire inflation pressure. To accomplish this during a balancing procedure introduces challenges: The optimization of pressure for the characteristics of the tire, vehicle, environmental conditions and operational circumstances may require frequent or exacting adjustments. The wide range of tire sizes and variations in construction stiffness make it difficult during a balancing procedure to prejudge how long to fill or release gas to reach a desired pressure, thereby involving costly time investments for precision.
Some common automatic pressure adjustment systems use mechanical valving/setting devices. Because the pressure reading instrument used by such devices is not located in the tire but rather upstream in the relatively restricted passages of the filling apparatus, a correct pressure reading can not be made during the actual filling. Hence, gas filling is performed in pulses to allow pressure reading between pulses. These systems operate by brute force trial and error without provision to compensate for differing degrees of mispressurization and are hence time wasting. The inability to improve efficiency by not learning from prior attempts or adjusting for differing tire volumes and stiffnesses can impose further delays. The mechanical nature of these devices also causes a substantial increase in the amount of time between fill stages as the tire pressure approaches the dialed in pressure. Finally, the accuracy of such systems is typically marginal, requiring continuous rechecking with a separate gauge.
Some prior art computer controlled pressure adjustment systems incorrectly assume a constant, linear relationship between the gasflow rate and the tire's physical characteristics. The tire's rate of pressurization vs. gasflow rate can vary, depending on the tire's pressure at a given moment. Such systems also assume constant gas supply pressure. Within a vehicle service center there are often multiple demands being put on a compressed gas supply system simultaneously. A computer controlled system can be greatly slowed in setting the pressure or inhibited from doing so accurately without the capacity to account for these changing conditions.